The present invention relates to methods and systems for controlling electric motors, and more particularly to methods and systems for generating modulation signals used for control of an electric motor.
A controller typically controls an electric motor by generating duty cycle signals for each motor phase, e.g., using pulse width modulation (PWM) techniques, which are used to provide phase voltage signals to the motor. For example, electric motors are generally controlled by a feedback system including a current regulator and a modulator that uses a sinusoidal PWM scheme to generate and transmit gate drive signals to a three-phase inverter (DC-AC converter). The inverter supplies voltage signals for each phase of an electric motor. The voltages produced by the inverter are heavily dependent on the inverter control scheme used, and sub-optimal techniques can result in undesirable torque ripple and audible noise in high performance applications such as electric power steering (EPS).
A current control mechanism is typically employed for controlling the electric motor, which may include a current regulator (which can have several different designs) operating on measured current feedback, but is not so limited. Other current control mechanisms may include feedforward current controllers that use a static or dynamic inverse machine model (or plant model in general, depending on the system being controlled). Such feedforward current control systems do not require measured current feedback.